Quantum well heterostructures are key components of many optoelectronic devices. Generally speaking, a quantum well heterostructure consists of thin layers of a narrower-gap semiconductor material disposed between thicker layers of a wider-gap material. Quantum interference effects begin to appear prominently in the motion of the electrons at the interfaces, and the band profile shows a series of “wells.”
Quantum-well infrared photodetectors have been used successfully in infrared detectors. Infrared photons excite ground state electrons out of a stack of quantum wells in a quantum-well infrared photodetector, producing a photocurrent in an applied electric field. When a photon strikes the well it excites an electron in the ground state to a first excited state, then an externally applied voltage sweeps the photoexcited electron out, producing a photocurrent. This photocurrent in the applied electric field can be sensed, thereby detecting the presence of infrared photons. By placing a large number of such quantum-well infrared photodetectors in a two-dimensional array and optically coupling the array to the field of view, infrared imaging is possible.
Quantum-well photodetectors which sense a photocurrent in an applied electric field suffer significant drawbacks in the form of dark current effects, i.e., the current that flows through a biased semiconductor when no photons are impinging upon it. Because dark current effects are temperature sensitive, the photodetector must be cooled in order to function accurately, or other elaborate measures must be taken to counteract dark current effects.
Thus there is a need for a quantum-well photodetector which avoids the drawbacks of dark current effects. There is a further need for a quantum-well photodetector which does not require cooling or other elaborate precautions to compensate for dark current effects.